Coming out of fall camp in 2012, Dontrell Onuoha earned the starting job at defensive end, and kept his spot through the first four games.

Then, mysteriously, he left the team for three weeks.

Rocky Long said Onuoha was away dealing with “personal issues,” but always declined to elaborate beyond that.

Onuoha eventually returned, but had to sit out the next three games as part of the deal he’d struck with Long.

Onuoha never played again for the remainder of the season, and his strange absence, coupled with a misdemeanor assault charge that he pled guilty to in May 2012, have given the player something of a bad reputation.

Onuoha declined to address the nature of his absence last season, saying only that it was a personal issue and that he and Long mutually agreed that it would be good for him to take some time off.

He said he wasn’t himself when he started the season last year.

“My mindset was halfway there, and you definitely can’t play with your mind halfway there,” Onuoha said. “I could tell (my mind) was between back home and here. I wasn’t playing my best in camp, and I don’t want to be playing like that on the team.

“It’s all about the team. If I’m gonna be hurting the team, I don’t want to be out there.”

So after getting Long’s permission to leave, he spent the next three weeks going back and forth between San Diego and his home in Indio.

When he returned, he’d lost his starting spot to Cody Galea, and had to sit out three games before Long would clear him to rejoin the team.

Onuoha said it was difficult to sit on the sidelines and watch his teammates.

Last year was a rough one for him, and he wants to change people’s perception of him as he enters his junior year.

“I feel like I have a big monkey on my back,” Onuoha said. “I was starting last year, and then, you know, I left at the end of the season with a big chip on my shoulder, like I’ve got something to prove.”

This year, he’s out to show that he can contribute to the team.

Circumstance has given him that opportunity.

Backup nose tackle Dan Kottman is out two to three weeks with a sprained foot, and in his absence, Onuoha has been moved from defensive end to the No. 2 nose tackle spot behind Sam Meredith.

Long said he was a perfect fit for the position because even though the Aztecs prioritize speed over size in their 3-3-5 scheme, they like the nose tackle to be a bigger guy.

“If anybody has to be big, it’s our nose tackle because he gets double-teamed a lot,” Long said. “So the best defensive lineman we have with size and athletic ability is Dontrell.”

Onuoha has gained 15 pounds of muscle since 2012, and he stands at a robust 6-foot-2, 285-pounds.

Even before Kottman’s injury, Onuoha said he went into camp knowing that the coaches might move him to nose tackle, and had studied the playbook to learn his new responsibilities.

“Nose tackle is a lot more demanding on your body,” Onuoha said. “You’re taking up double teams, triple teams, getting beat up on every play. It’s tough on your body.”

But you still have to be able to move.

The Aztecs don’t recruit the prototypical 300-pound monster-sized run stoppers that you see at Alabama or Stanford.

“It’s more of a (moving) line,” said Meredith, who started every game at nose tackle last season. “We’re not really big guys plugging up holes.

“We’re guys shooting gaps and bringing blitzes, so the defensive line has to move out of the way. It’s just quicker pacing, having three guys on the line.”

None of the Aztecs’ starting defensive linemen weigh more than 280 pounds, and that’s by design.

“We believe in quickness and athletic ability more than size,” Long said. “We don’t want a guy to just take up space.”

In Onuoha, the Aztecs think they’ve found a good blend of speed and heft, and until Kottman returns, he gets a chance to prove his worth as the main backup at nose tackle and defensive end.